The azygos vein usually begins from the posterior aspect of the inferior vena cava, at the level of the renal veins. It usually originates in the lumbar level, but may originate further up.

The vein ascends and reaches the thoracic cavity passing behind the right crus of the diaphragm or via the aortic hiatus. It ascends within the posterior mediastinum - usually to the right of the thoracic duct - reaching the level of vertebra T4 and then arches above the right pulmonary hilum. It drains into the superior vena cava just before it pierces the pericardial sac.

Relations to other structures

Posterior to the azygos vein, lie the following structures: the anterior longitudinal ligament, right posterior intercostal arteries, and bodies of vertebrae T4-T2.

In the posterior thorax, the azygos vein is located posterior to the recess of the right pleural sac and the esophagus.

Medial to the vein, the following structures can be found: the thoracic duct, aorta, esophagus, trachea, and right vagus nerve.

And laterally to the azygos vein are the following structures: the right greater splanchnic nerve, lung, pleura.

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Azygos vein